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of the graduated tubular portion, a cork pierced by a small 

 tube, open at both ends, was inserted, and this tube was 

 then connected with the orifice of a table air-pump usually- 

 occupied by a syphon gauge. The stop-cock was now con- 

 nected with one end of a long tube, packed with fragments 

 of fused caustic potash, while the other end of this tube was 

 attached by means of a slip of caoutchouc to a second tube 

 passing through an air-tight cork fixed in one of the mouths 

 of the bottle, at present used for the inhalation of chlorine. 

 This bottle being charged with oil of vitriol, and the orifice 

 of the plate of the pump being closed, the pump was worked, 

 and a current of air was thus drawn through the glass vessel 

 for about fifteen minutes, which in passing through the oil 

 of vitriol, and over the fused potash, was deprived of all hy- 

 grometric moisture. The included air being now absolutely 

 dry, the stopcock was closed, and the small tube connecting 

 the air vessel with the pump having been drawn out in the 

 middle, and sealed hermetically by means of a spirit lamp, 

 the air apparatus was separated from the potash tube, and 

 transferred to a tall jar containing mercury, after which the 

 sealed end of the small glass tube was broken beneath the 

 surface of the quicksilver. The apparatus, however, being 

 now completely filled, it became necessary to remove some 

 of the air, and this was done by opening the stopcock very 

 gradually, care being taken that during this manipulation the 

 external mercury should be higher than its level within the 

 tubular portion. The entire was then placed in a small 

 room, the temperature of which was found not to vary more 

 than one degree Fahrenheit during the twenty-four hours, 

 the stopcock having been first attached to one extremity of 

 a string, which was carried over a fixed pulley placed in 

 the ceiling, and whose other end carried a counterpoise by 

 which the air vessel was kept in a vertical position, and the 

 observer was enabled readily to bring the mercury within 



